Mobile traffic has been growing at a very fast pace. More and more nontraditional types of devices that communicate with each other, such as monitoring devices, meter reader, etc., are emerging. These machine to machine (M2M) and internet of things (IoTs) emerging end devices are expected to grow to 10 to 100 billion in next few years. These small form factor devices need to be very simple to be cost effective and to yield long battery life (>10 years). These devices most likely do not have IP protocol stack and IP addresses. In addition, these M2M and IoT devices normally send very small amount data.
Traditionally, each time a mobile device sends packets, the 3GPP signaling procedure sets up a dedicated radio bearer and dedicated GPRS Tunneling protocol (GTP) tunnel to carry these packets. A bearer service is a link between two points, which is defined by a certain set of characteristics. GTP is an IP/UDP based protocol used in GSM, UMTS and LTE core networks. It is used to encapsulate user data when passing through core network and also carries bearer specific signaling traffic between various core network entities. Whenever a User equipment (UE) is being provided with any service (e.g. circuit switched (CS) or packet switched (PS) service), the service has to be associated with a radio bearer specifying the configuration for Layer-2 and Physical Layer in order to have its quality of service (QOS) clearly defined. Typically IP packets sent by a UE are delivered through a GTP tunnel, that is the IP packets are delivered from an eNodeB to a packet data network gateway (P-GW) regardless of their specified destination IP address. Signaling overhead to set up these GTP tunnels are substantial requiring more bytes than the IoT user data itself.
3GPP Narrow-band IoTs (NB-IoTs) use the following mechanism for UE data delivery. First, user data will be transmitted through data over non-access stratum (NAS) messages (as unstructured data) or through a short message service (SMS) application over NAS message (as structured data) using NAS signaling connection, since the IoT user data is small enough to use the NAS encapsulation. As a background, today for the NAS signaling, the eNB sets up SRB1 (signaling radio bearer 1, for radio resource control (RRC) messages, which may include a piggybacked NAS message) and SRB2 (for NAS messages, using a dedicated control channel (DCCH)) for carrying the signaling messages. SRB 1 is used when the NAS messages are piggy-backed in the RRC establishment, release and modification messages. SRB2 is used when the NAS message is independently sent from/to a mobility management entity (MME) to/from UE. In general, SRB2 is set up when the data radio bearers (DRBs) are established. On the S1-MME interface, the user signaling is identified by the logical S1 application protocol (S1AP) connection dedicated to the user.
Second, the simplification for the NB-IoT with the Non-IP solution in 3GPP is that the user data is sent in the Radio Resource Control (RRC) establishment message. So only the SRB1 is used. On the S1-MME (mobility management entity) interface, (the S1 interface is the interface between the LTE RAN and evolved packet core) the dedicated S1AP logic connection is still needed to be set up. The MME then reads the NAS message, which include the UE S-TMSI (SAE-Temporary Mobile Subscriber Identity) of the UE. Then MME can map the S-TMSI to the UE true IMSI (International Mobile Subscriber Identity), MSISDN (Mobile Station International Subscriber Directory Number) and IMEI (International Mobile Equipment Identity) and send the NAS message to the Service Creation Environment Function (SCEF) function over a TS6a interface, which is a diameter interface. Diameter interfaces provide connection among Diameter nodes to enable essential service provider network functions such as authentication, online and offline billing, and policy and charging.
Third, even though user bearer setup is not needed for IoT data delivery, the problem is shifted to the signaling plane. The network could run into scalability issue of the signaling channel when the network needs to support 10's of billions of IoT devices. Also, the signaling path is still connection-oriented, i.e. to set up signaling bearers, such as SRB0, SRB1, SRB2, with multiple logical connections and temporary UE ids assigned by multiple network elements, e.g. MME, eNB, etc.
Consequently, there is still a need to efficiently deliver packets from M2M and IoT devices.